I would assume that the under floor brake booster would be the culprit. With your manual, the clutch pedal would likely "be in the way" of the brake boaster and you would have to heavily modify the clutch pedal to make it work with the booster. I haven't done this install but am curious as I may be doing it down the road in my 1/2 ton as well.

1970 Chevrolet C10
Grandpa's -- My first truck -- In progress to shiny
Follow the build in the Project Journal
1950 Chevrolet 1-Ton Dually
"Ole Red Girl"
In the Stovebolt Gallery
More pictures here
1951 GMC 9430 1 ton dually--Shiny! | 1972 Chevrolet C20- Rusty- the puzzle box lid for the C10 | 1962 AMC Rambler American- my wife's
Parts trucks-
1951 GMC 9300 | 1951-GMC 9430 | 1951- Chevrolet 1300